Radiation area monitor device and method

ABSTRACT

A radiation area monitor device/method, utilizing: a radiation sensor having a directional radiation sensing capability; a rotation mechanism operable for selectively rotating the radiation sensor such that the directional radiation sensing capability selectively sweeps an area of interest; and a processor operable for analyzing and storing a radiation fingerprint acquired by the radiation sensor as the directional radiation sensing capability selectively sweeps the area of interest. Optionally, the radiation sensor includes a gamma and/or neutron radiation sensor. The device/method selectively operates in: a first supervised mode during which a baseline radiation fingerprint is acquired by the radiation sensor; and a second unsupervised mode during which a subsequent radiation fingerprint is acquired by the radiation sensor, wherein the subsequent radiation fingerprint is compared to the baseline radiation fingerprint and, if a predetermined difference threshold is exceeded, an alert is issued.

CROSS-REFERENCE TO RELATED APPLICATION

The present patent application/patent is a divisional of co-pending U.S.patent application Ser. No. 15/485,373, filed on Apr. 12, 2017, andentitled “RADIATION AREA MONITOR DEVICE AND METHOD,” the contents ofwhich are incorporated in full by reference herein.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The U.S. Government has rights to the present disclosure pursuant toContract No. DE-NA0001942 between the U.S. Department of Energy andConsolidated Nuclear Security, LLC.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to a radiation area monitordevice and method. More specifically, the present invention relates to aradiation area monitor device and method for introducing, locating,relocating, and/or removing a gamma and/or neutron emitting material.

BACKGROUND OF THE DISCLOSURE

The monitoring of radioactive materials is of critical importance inmany fields. Radioactive material accounting and control is oftenrequired by law and/or treaty. However, radioactive material monitoringis typically performed indirectly, by the observation of storagecontainers or the logging of RFID tags placed on the storage containers.In such situations, it is possible that radioactive material is removedwhile a storage container remains. Thus, it is not recognized thatradioactive material is actually gone.

Thus, what are still needed in the art are devices and methods fordirectly monitoring the presence/location of a radioactive material bymonitoring gamma and/or neutron emission from the radioactive materialin real time. Preferably, these devices and methods would generate andutilize a three-dimensional (3D) map of a storage area and monitorchanges over time with an alarm triggered by predetermined changes.

BRIEF SUMMARY OF THE DISCLOSURE

In various exemplary embodiments, the present disclosure provides aradiation area monitor device and method for directly monitoring thepresence/location of a radioactive material by monitoring gamma and/orneutron emission from the radioactive material in real time. Theradiation area monitor device and method generates and utilizes a 3D mapof a storage area and monitor changes over time with an alarm triggeredby predetermined changes.

In one exemplary embodiment, the present disclosure provides a radiationarea monitor device, including: a radiation sensor; a rotating radiationshield disposed about the radiation sensor, wherein the rotatingradiation shield defines one or more ports that are transparent toradiation; and a processor operable for analyzing and storing aradiation fingerprint acquired by the radiation sensor as the rotatingradiation shield is rotated about the radiation sensor. Optionally, theradiation sensor includes a gamma sensor. Optionally, the radiationsensor includes a neutron sensor. Optionally, the radiation sensorincludes a dual gamma/neutron radiation sensor. The radiation areamonitor device is operable for selectively operating in: a firstsupervised mode during which a baseline radiation fingerprint isacquired by the radiation sensor as the rotating radiation shield isrotated about the radiation sensor; and a second unsupervised modeduring which a subsequent radiation fingerprint is acquired by theradiation sensor as the rotating radiation shield is rotated about theradiation sensor, wherein the subsequent radiation fingerprint iscompared to the baseline radiation fingerprint and, if a predetermineddifference threshold is exceeded, an alert is issued. The radiation areamonitor device further includes a rotation mechanism coupled to therotating radiation shield operable for selectively rotating the rotatingradiation shield disposed about the radiation sensor.

In another exemplary embodiment, the present disclosure provides aradiation area monitor method, including: providing a radiation sensor;rotating a rotating radiation shield disposed about the radiationsensor, wherein the rotating radiation shield defines one or more portsthat are transparent to radiation; and analyzing and storing a radiationfingerprint acquired by the radiation sensor as the rotating radiationshield is rotated about the radiation sensor. Optionally, the radiationsensor includes a gamma sensor. Optionally, the radiation sensorincludes a neutron sensor. Optionally, the radiation sensor includes adual gamma/neutron radiation sensor. The radiation area monitor methodis operable for selectively operating in: a first supervised mode duringwhich a baseline radiation fingerprint is acquired by the radiationsensor as the rotating radiation shield is rotated about the radiationsensor; and a second unsupervised mode during which a subsequentradiation fingerprint is acquired by the radiation sensor as therotating radiation shield is rotated about the radiation sensor, whereinthe subsequent radiation fingerprint is compared to the baselineradiation fingerprint and, if a predetermined difference threshold isexceeded, an alert is issued. The radiation area monitor method furtherincludes selectively rotating the rotating radiation shield disposedabout the radiation sensor using a rotation mechanism coupled to therotating radiation shield.

In a further exemplary embodiment, the present disclosure provides aradiation area monitor device, including: a radiation sensor having adirectional radiation sensing capability; a rotation mechanism operablefor selectively rotating the radiation sensor such that the directionalradiation sensing capability selectively sweeps an area of interest; anda processor operable for analyzing and storing a radiation fingerprintacquired by the radiation sensor as the directional radiation sensingcapability selectively sweeps the area of interest. Optionally, theradiation sensor includes a gamma sensor. Optionally, the radiationsensor includes a neutron sensor. Optionally, the radiation sensorincludes a dual gamma/neutron radiation sensor. The radiation areamonitor device is operable for selectively operating in: a firstsupervised mode during which a baseline radiation fingerprint isacquired by the radiation sensor as the directional radiation sensingcapability selectively sweeps the area of interest; and a secondunsupervised mode during which a subsequent radiation fingerprint isacquired by the radiation sensor as the directional radiation sensingcapability selectively sweeps the area of interest, wherein thesubsequent radiation fingerprint is compared to the baseline radiationfingerprint and, if a predetermined difference threshold is exceeded, analert is issued.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is illustrated and described herein withreference to the various drawings, in which like reference numbers areused to denote like device components/method steps, as appropriate, andin which:

FIG. 1 is a schematic diagram illustrating one exemplary embodiment ofthe radiation area monitor device of the present disclosure; and

FIG. 2 is a series of flowcharts illustrating two exemplary embodimentsof the method for locating a radiation emitting source of the presentdisclosure, highlighting a supervised mode and a locked mode.

DETAILED DESCRIPTION OF THE DISCLOSURE

Referring now specifically to FIG. 1, in one exemplary embodiment, thepresent disclosure provides a radiation area monitor device including agamma and/or neutron sensor 2 that is coupled to appropriate electronics1. A motorized rotating shield 4 including one or more radiationtransparent windows or ports is disposed and rotates about the sensor(s)2 and electronics 1. Advantageously, the device can be coupled to asurface 3, such as a floor, ceiling, wall, or other structure, in amonitoring area of interest. In this manner, the azimuthal spatialdistribution of a gamma and/or neutron emitting source in the monitoringarea of interest with respect to a plane that the device is coupled tocan be determined by evaluating and monitoring the temporal evolution ofa count rate signal from the sensor(s) 2 as the shield (4), and theassociated window(s) or port(s), are rotated about the sensor(s) 2.

The sensor(s) 2 can include separate gamma and/or neutron detectors asassociated photodetectors, for example, or a single detector can be usedfor gamma and neutron detection. The gamma detector should be solidstate and be of sufficient size and density to absorb a majority of theincident gamma rays of interest. The neutron detector should also besolid state and be of sufficient size and density to absorb a majorityof the incident neutrons of interest. Such crystals can bescintillating, semiconducting, or charge collecting. Exemplary gammamaterials include NaI, CsI2, BGO, SrI2, CZT, HPGe, LaBr, LYSO, CdWO4,BaF2, activated acrylates, or the like. Exemplary neutron materialsinclude acrylic, LiInSe2, BP, BN, LiF, CdS, ZnSe, CdWO4, Gd2SiO5, CLYC,a Si-coated material, or the like. Preferably, the detection crystal hasat least one detector directly or indirectly coupled to its surface,such as a PMT, SiPM, or APD photodetector or the like.

The sensor(s) 2 are disposed within the shield 4, which rotates aboutthe sensor(s) 2 such that the window(s) or port(s) periodically exposethe sensor(s) 2 to incident radiation from the radiation source. Anysuitable motorized rotation mechanism can be utilized to rotate theshield 4. Accordingly, the sensors(s) 2, shield 4, and rotationmechanism can all be coupled to and/or disposed within an appropriatehousing (not illustrated) that can be permanently or removably coupledto the surface 3. In an alternative exemplary embodiment, the shield 4can be stationary and a directionally biased sensor 2 can rotate withinthe shield 4. In such an alternative embodiment, when the sensor 2 isdirectionally biased, the shield 4 may not be necessary, as the rotationof the sensor 2 itself would generate the desired periodicity. Further,a directionally biased sensor 2 could be created by rotating the sensor2 and the shield 4 in unison. An exemplary rotational speed for theshield 4 is under about 1 Hz, or 1 rotation every second. Thisrelatively low revolution frequency is desirable in cases where theshield 4 cannot be made to have an axially symmetric moment of inertia.The window(s) or port(s) may be physical voids in the shield 4 or mayincorporate a radiation transparent material. A substantiallycylindrical shield 4 is illustrated in FIG. 1, however, other suitableshapes can also be utilized, such as a rotating plate, for example. Theshield 4 can be made of any suitable gamma ray absorbing material, suchas a lead or tungsten, or a neutron absorbing material, such as 6Li,HDPE, or cadmium, or in a combination, such as lead lined with 6Li foil.Similarly, tungsten could be used to absorb both. These shield materialsmust not create additional radiation emission as the result of shieldingincident radiation. In another exemplary embodiment, the rotating shield4 could be of a more complex shape, to form a coded aperture, which incombination with the rotation, could allow for a computed reproductionof a rudimentary image of the monitored area.

The sensor(s) 2 and/or electronics 1 are coupled to a processor 5 forcollecting and analyzing the azimuthal spatial distribution of the gammaand/or neutron emitting source in the monitoring area of interest byevaluating and monitoring the temporal evolution of the count ratesignal from the sensor(s) 2 as the shield (4), and the associatedwindow(s) or port(s), are rotated about the sensor(s) 2. In this manner,a 3D area sweep map can be created and stored, and then an alarm can beraised if the area sweep map changes in excess of a predeterminedthreshold amount, indicating the potentially problematic movement of theradiation source itself. Alarm thresholds can be set above backgroundfluctuations, but below the radiation flux of a single object so thatany movement of the object raises an alarm. An (optical) angular encodermay enable the processor 5 to correlate, at each time, absolute angularshield position and a signal from the sensor(s) 2.

Referring now specifically to FIG. 2, in two exemplary embodiments, theradiation monitor device can selectively operate in one of two modes:Mode 1—Supervised Mode or Mode 2—Locked Mode.

In the supervised mode, a user is preferably required to continuously(or nearly continuously) prove their presence in the area of interest bycryptographic or other means (Block 11) while the device “learns” thegamma and/or neutron fingerprints in the area of interest (Block 12).Ultimately, these fingerprints are stored as a baseline for latercomparisons (Block 13). This operation mode is used, for example, duringor immediately after the movement of detectable material and/or itemsthat could significantly shield or otherwise alter the radiation fieldfrom the detectable material. At the end of the “learn” period, thefingerprints can be cryptographically signed and stored locally and/orremotely (Block 13).

In the locked mode, the device continuously (or nearly continuously)measures and monitors the spatial radiation field fingerprint in thearea of interest (Block 14). The acquired fingerprint is compared to thestored fingerprint, again, either locally and/or remotely (Block 15). Ifthe comparison is performed locally, the device either keeps sending“OK” messages to a central system or is capable or responding to aremote query. If the comparison is performed remotely, the newlyacquired fingerprint is sent instead. In either case, it may bedesirable for communications between the device and the central systemto be cryptographically signed for security purposes. If a statisticallysignificant deviation from baseline is detected, then the device stopssending “OK” messages (and/or confirming normal status upon query)and/or an alarm condition is raised, depending on the given architecturechosen (Block 16). A general communications status alarm may also beutilized.

Thus, the radiation monitor device is used to make radiation fieldcomparisons over time such that central decision-making can be madeimmediately aware of changes in or movements of radiation sourcematerial. The device can be used in unknown areas—to gather informationrelated to radiation source material—or it can be used in known areas(such as storage facilities)—to alert personnel to any changes ormovements due to leakage, sabotage, theft, etc. This capability iscrucial to any organization that stores radioactive material or requiresinformation regarding the presence of radioactive material in an area.It should be noted that a coordinated array of devices can also beutilized for best results in some circumstances.

Although the present invention has been illustrated and described hereinwith reference to preferred embodiments and specific examples thereof,it will be readily apparent to those of ordinary skill in the art thatother embodiments and examples may perform similar functions and/orachieve like results. All such equivalent embodiments and examples arewithin the spirit and scope of the present invention, are contemplatedthereby, and are intended to be covered by the following non-limitingclaims.

What is claimed is:
 1. A radiation area monitor device, comprising: aradiation sensor having a directional radiation sensing capability; arotation mechanism operable for selectively rotating the radiationsensor such that the directional radiation sensing capabilityselectively sweeps an area of interest; and a processor operable foranalyzing and storing a radiation fingerprint acquired by the radiationsensor as the directional radiation sensing capability selectivelysweeps the area of interest; wherein the radiation sensor comprises oneor more of a gamma sensor and a neutron sensor.
 2. The radiation areamonitor device of claim 1, wherein the radiation sensor comprises a dualgamma/neutron radiation sensor.
 3. The radiation area monitor device ofclaim 1, wherein the radiation area monitor device is operable forselectively operating in: a first supervised mode during which abaseline radiation fingerprint is acquired by the radiation sensor asthe directional radiation sensing capability selectively sweeps the areaof interest; and a second unsupervised mode during which a subsequentradiation fingerprint is acquired by the radiation sensor as thedirectional radiation sensing capability selectively sweeps the area ofinterest, wherein the subsequent radiation fingerprint is compared tothe baseline radiation fingerprint and, if a predetermined differencethreshold is exceeded, an alert is issued.
 4. A radiation area monitormethod, comprising: providing a radiation sensor having a directionalradiation sensing capability; providing a rotation mechanism operablefor selectively rotating the radiation sensor such that the directionalradiation sensing capability selectively sweeps an area of interest; andanalyzing and storing a radiation fingerprint acquired by the radiationsensor as the directional radiation sensing capability selectivelysweeps the area of interest; wherein the radiation sensor comprises oneor more of a gamma sensor and a neutron sensor.
 5. The radiation areamonitor method of claim 4, wherein the radiation sensor comprises a dualgamma/neutron radiation sensor.
 6. The radiation area monitor method ofclaim 4, wherein the radiation area monitor device is operable forselectively operating in: a first supervised mode during which abaseline radiation fingerprint is acquired by the radiation sensor asthe directional radiation sensing capability selectively sweeps the areaof interest; and a second unsupervised mode during which a subsequentradiation fingerprint is acquired by the radiation sensor as thedirectional radiation sensing capability selectively sweeps the area ofinterest, wherein the subsequent radiation fingerprint is compared tothe baseline radiation fingerprint and, if a predetermined differencethreshold is exceeded, an alert is issued.